This invention relates to fluid sterilization apparatus of the type for treating potable water or other fluids with radiant energy from an ultraviolet lamp.
It is well known that the quality of potable water varies widely from city to city around the world. Indeed, the quality can vary significantly from place to place within a given city. To address this issue, numerous water treatment systems have been designed for domestic home use: A typical system may include a water filter for removing particulates and organic contaminants from the water, an ultraviolet lamp for irradiating the water with ultraviolet energy to kill contaminants in the water, a subsystem for operating and monitoring the operation of said system, and structures for housing such components. Often, such systems are designed to sit on a countertop in the user""s home where they are connected to a public utility or other municipal water supply. For example, see U.S. Pat. No. 5,698,091 (Kuennen et al.) granted on Dec. 16, 1997.
It is also well known that the quality of potable water carried on board passenger vehicles such as aircraft, trains and ships can vary significantly: for example, see Weisel, Al xe2x80x9cDirty Waterxe2x80x94Our investigation into water on airplanes will make you think before your drinkxe2x80x9d, Travel and Leisure, December 1998, pages 139-142. In the case of such vehicles, the quality of potable water will depend not only on the source from whence the water came, but also on the integrity of on board storage tanks and supply lines where contamination may result from microorganism growth or biofilm buildup.
Accordingly, just as it is desirable to provide for the treatment of potable water in the home, it is desirable to provide for the treatment of potable water carried on board vehicles. However, the working environment to be found on board a vehicle may differ significantly from that to be found in the home. A water treatment system or components thereof that function reliably and well in the home may not function at all well in a mobile working environment.
As will now be described, the present invention focuses on one such area of limitation. More particularly, it focuses on sterilization apparatus that may be used in the treatment of water or other fluids with radiant energy from an ultraviolet lamp.
As the prior art reveals, such apparatus commonly includes an outer housing having first and second ends, a hollow cylindrical portion extending between such ends, and a coaxially aligned inner housing, the latter of which is designed to hold an ultraviolet lamp. The housings are sized to define an elongated annular region or chamber between the housings. As fluid flows from an inlet at one end of the chamber to an outlet at the opposed end, it is exposed to ultraviolet energy that emits from the lamp into the annular chamber through a wall of the inner housing which transmits ultraviolet light.
In such apparatus, the desirability of maintaining the fluid for an extended period of time within the field of view of the radiation is well known. If microbiological contaminants are present, then the probability of killing such contaminants will be enhanced. Consequently, various means have been devised to achieve this result.
For example, U.S. Pat. No. 4,008,045 (David Free) granted on Feb. 15, 1977, describes an ultraviolet sterilizer that includes a diffuser plate through which fluid in the an annular chamber must pass as it flows from an inlet at one end of the chamber to an outlet at the other. The diffuser serves to impart turbulence and a spiral flow to the fluid thereby increasing the distance that a given control volume of fluid will travel while flowing from the diffuser to the chamber outlet.
However, it has been found that the pressure drop or head loss that occurs across such diffusers is relatively high. This can be disadvantageous if the fluid supply pressure is concurrently limited and it is desired to maintain a minimal water flow rate. More particularly, it may be observed that in a home use environment the input water pressure from a public utility or municipal water source typically may be of the order of 100 psig. If so, then the pressure drop across a diffuser in an ultraviolet sterilization chamber tends not to be an issue. In contrast, and although there may be some exceptions, the pressure produced by a water pump on a passenger aircraft may typically be only 45 psig or lowerxe2x80x94sometimes as low as 20 psig. For a desired water flow rate through an ultraviolet sterilizer, such low pressures may preclude the use of a diffuser or, alternately, may preclude the use of other water treatment devices which themselves cause a pressure drop (e.g. a water filter) in the path of water flow.
As a further example, U.S. Pat. No. 4,141,686 (Lewis) granted on Feb. 27, 1979, describes an ultraviolet sterilizer that includes a fin which imparts turbulence to water as it flows into the annular chamber of the sterilizer. While it may be remarked that the pressure drop induced by the fin described by Lewis is likely to be minimal, and while it may also be remarked that turbulence is desirable, it must also be remarked that Lewis"" fin is not well adapted to induce a desirable spiral flow. Apart from turbulence, a significant volume of the water that enters the annular chamber may follow a relatively short path (sometimes referred to as a short circuit path) rather than a spiral path to the chamber outlet. Thus, the water""s exposure to ultraviolet radiation is undesirability limited.
As a more recent example, Kuennen et al., supra, describe a diverter plate and baffle arrangement that serves to impart a spiral flow within the annular chamber of an ultraviolet sterilizer. However, it is noted that they specifically contemplate a high pressure home use environment, and it is anticipated that a significant pressure drop would occur, particularly across the baffle which may be compared with the diffuser of Free. The diverter plate and baffle arrangement is described in more detail in U.S. Pat. No. 5,393,419 (Tiede et al who are part of Kuennen et al.) granted on Feb. 28, 1995.
Kuennen et al. also point out that other embodiments may by used to impart a spiral flow to water passing through their annular chamber. They indicate that a spiral glass or polymeric (e.g. TEFLON(copyright)) tube may be coiled about the ultraviolet lamp with a spiral pitch from the water inlet end of the chamber to the water outlet end, and that such material has adequate ultraviolet transmissibility to achieve excellent kill rates. However, even assuming that ultraviolet transmissibility is normally adequate, there are disadvantages. Firstly, there would be a relatively high pressure drop across the coil by reason of the added surface area presented by the surfaces of the coil over the length of the coil. Secondly, it has to be recognized that sediment can build up on all surfaces over which water flows. In a case where a coil as suggested by Kuennen et al. is used, this would include not only the wall surfaces of the annular chamber, but also on the surfaces defining the coil. Sediment build up on the walls of the coil could very well impair the transmissibility of coil material that otherwise might demonstrate adequate ultraviolet transmissibility.
Accordingly, a primary object of the present invention is to provide new and improved apparatus for treating water or other fluid with radiant energy from an ultraviolet lamp in circumstances where the available fluid pressure is relatively low.
In a broad aspect of the present invention, there is provided apparatus for treating water or other fluid with radiant energy from an ultraviolet lamp, such apparatus comprising an outer housing comprising first and second ends and an elongated hollow cylindrical portion extending between the ends peripherally around a longitudinal axis of the cylindrical portion, and a hollow cylindrical inner housing for housing the ultraviolet lamp. The inner housing is supported by the ends of the outer housing and extends coaxially within the cylindrical portion of the outer housing so as to define an elongated annular chamber between the housings. At least a substantial portion of the length of the inner housing is formed from material, preferably quartz, which is sufficiently transmissible to permit ultraviolet energy radiating from the lamp to pass through the inner housing into the chamber and thereby irradiate fluid flowing through said chamber. The apparatus further comprises a fluid inlet conduit extending through the first end of the outer housing from a fluid inlet port to the annular chamber, and a fluid outlet conduit extending through the second end of the outer housing from the annular chamber to a fluid outlet port. The fluid inlet conduit serves to receive fluid from an external source and to direct such fluid to the annular chamber. Conversely, the fluid outlet conduit serves to discharge fluid from the annular chamber. Further, the apparatus includes a helical shaped input fluid flow guide or helical ramp for imparting input spiral flow momentum to fluid upon entry to the annular chamber from the fluid inlet conduit. Preferably, it also includes a corresponding helical shaped output fluid flow guide or helical ramp for imparting output spiral flow momentum to fluid approaching discharge from the chamber through the fluid outlet conduit.
The input fluid flow guide or ramp is disposed within the annular chamber and extends longitudinally therein from the first end of the outer housing for a relatively short distance. Conversely, the output fluid flow guide or ramp, which is also disposed within the annular chamber but relatively far from the input flow guide or ramp, extends longitudinally from the second end of the outer housing for a relatively short distance.
In contrast to diffusers, baffles, or helical shaped guides that extend continuously for substantially the full length of an annular chamber, all of which may offer relatively high resistance to fluid flow and may present other disadvantages, the helical shaped guides as specified herein offer relatively low resistance. Yet, it has been found that they can serve to impart a significant and desirable spiral flow momentum to the fluid.
Preferably, a helical guide or ramp will have an inner radius substantially corresponding to an outer radius of the inner housing and an outer radius substantially corresponding to an inner radius of the outer housing. Otherwise some fluid may flow around the sides of the guide or ramp with little or no spiral momentum.
The foregoing and other features of the present invention will now be described with reference to the drawings.